Papers by Keyword: Crystallography

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Authors: Hai Long Zhu, Hong Hui Tong, Fa Zhan Yang, Qin Wang, Chang Ming Cheng
Abstract: To obtain high-performance alumina powder for high-tech application, a comparative study was carried out for the spheroidization of two types of alumina powder using radio-frequency argon-oxygen thermal plasma. The morphology, crystallography, and particle size distribution of spheroidized alumina powder were analyzed. The effect of feed rate on the spheroidization efficiency was investigated. The results show that when the powder flow rate was 35 g/min, the spheroidization efficiency reached up to 100%, and the alumina powder had perfect sphericity, while the spheroidization efficiency decreased with increasing powder flow rate. The X-ray diffraction analysis reveals that the spheroidized alumina powder had mixed crystal structures with a stable α phase and a part of metastable phase. The particle size distribution analysis shows that the particle size of the spheroidized alumina powder did not change obviously. These results will help us to better understand the process engineering of the spheroidization of ceramic powder using radio-frequency argon-oxygen thermal plasma, and provide simultaneously technical assistance for industrialization.
Authors: Christian Lexcellent, Elie Gibeau
Abstract: At first, some comments are made concerning the capacity of prediction of the microstructure for shape memory alloys by the Crystallographical Theory of Martensite. Secondly, the basic foundations of the phenomenological modeling of shape memory alloys behavior at the macroscopic scale are given. A special attention is devoted to the yield surface of phase transformation initiation in the stress space and its convex dual: the set of effective transformation strains in the strain space.
Authors: Michael E. Boiko, Andrei M. Boiko
Abstract: The project ISTC “SPECTROMETRIC POSITION SENSITIVE DETECTOR WITH BASE ENERGY SHIFT” is interesting for creation new area semiconductor detector device for EXAFS spectroscopy, for traditional X-ray diffractometry (XRD), as well as Small-Angle X-ray Scattering diffractometry (SASX). Diffractometry methods allow creating original features of position sensitive detector. Crystallography quality of silicon multi layer detector with original photo mask was examined by XRD and SAXS with ordinary scintillation detectors. Grazed incidence SAXS (GISAXS) provides information both about lateral and normal ordering of multilayers at a surface or inside a thin epitaxial film [1]. Using high-energy X-ray source (rotating anode or synchrotron radiation in future) and high adjustment monochromator SAXS rocking curves in transition and reflection mode had been received. It allows obtaining the information of 3D size lamellar or column-like domains. Results of an experimental investigation of the size layer structure are presented.
Authors: K.D. Patel, B.P. Modi, R. Srivastava
Authors: Jana Horníková, Pavel Šandera, Jaroslav Pokluda
Abstract: Nanoindentation is considered to be a very promising experimental approach to measuring the ideal shear strength since the stressed volume beneath the sharp indenter may be defect-free. The local shear component of the stress reaches its maximum value at some close distance from the indenter in the bulk. The value of the stress can reach the ideal shear strength and, consequently become high enough to nucleate dislocations. This process might be detected as a pop-in on the nanoindentation load-displacement curve. To model the nanoindentation test for that purpose, three different approaches have been used in this works. The first approach is based on the analytical Hertzian solution of the stress field beneath the nanoindenter where only a continuum mechanics is taken into account. The second concept is based on the numerical solution without crystallographic considerations and the third one respects the fact that the dislocation generation in the substrate is subjected to crystallographic rules. The aim of this article is to compare all these concepts by their application to the nanoindentation process performed on selected bcc and fcc metallic substrates.
Authors: Takeshi Teramoto, Masaki Tahara, Tomonari Inamura, Hideki Hosoda, Shuichi Miyazaki
Abstract: Composition dependence of the compatibility condition at junction plane (JP) (interface between habit plane variants (HV)) was evaluated by geometrically non-linear theory of martensite in Ti-Nb-Al shape memory alloys that have β (cubic) to α” (C-orthorhombic) martensitic transformation. The kinematic compatibility (KC) condition requires non-zero rotation of HV to form compatible JP; the angle of this rotation is termed θ. This means that the invariant habit plane (HP) and the compatible JP are not formed simultaneously. It turned out that twelve types of θ exist depending on the pair of HV. Composition dependence of each type of θ was systematically investigated. The previous results of transmission electron microscopy observations were also discussed in terms of the present results.
Authors: Qing Wu Wang, Mao Pang, Shi Hui Zhang
Abstract: Single crystal nickel base superalloys, such as Chinese material DD6 have been used in gas turbine blade in China more and more widely. In order to make better use of single crystal superalloys with many excellencies, constitutive models have been developed. In this paper, general method of crystallographic constitutive modeling was summarizes and a new constitutive model, based on crystallographic theory was proposed with phenomenological models' advantages. Based on crystallographic slip system principle, the basic slip-based viscoplasticity theory equations were set up on 12 octahedral slip systems and 6 cubic slip systems, total 18 slip systems. In micro-level slip system, the general unified constitutive formulations were used as the flow equations and hardening law. In the model, scalar forms were applied for constitutive equations on slip systems and the number and types of active slip systems were used to describe the material anisotropy, which was satisfied automatically by slip systems not anisotropic tensors and. The experimental and calculation results of two kind single crystal superalloys PWA1480 and DD6 were compared. The model had the capability to predict many mechanical response and analyze structure of single crystal superalloys. The modeling procedures and results showed that this crystallographic model had more clear physical meaning and was exact.
Authors: Hitoshi Ohsato
Abstract: This article summarizes the work of the author’s lab based on crystallography. The topics are categorized in the following three fields: The first category is crystallographic analysis of materials, the second one is correlations between crystal structure and their properties, and the third one is crystallography for processing such as epitaxy, topotaxy and templates. The examples for these categories are: (1) multilayer ceramic capacitor (MLCC); (2) microwave dielectrics of tungstenbronze-type like solid solutions, and piezoelectric materials langasite (La3Ga5SiO14); (3) thin film growth of GaN or AlN on sapphire for example of epitaxy, hydroxy-apatite grown on diopside for topotaxy, and template growth of microwave dielectrics for template. Crystallography is useful in all studies, but is not almighty. Interdisciplinary study between crystallography and solid state physics is necessary to make clear the mechanism of the properties.
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